Biodiesel obtained from oils of vegetable origin (for example soya oil and palm oil) has solid particles that arose from the metabolism of the plants from which it originated. These particles are observed even up to temperatures above the cloud point of biodiesel obtained from soya oil and palm oil, a phenomenon that is characterized by the appearance of tiny solid particles in suspension, leading to the formation of a cloud and a consequent increase in the turbidity of the biodiesel generated. With the passage of time, and when at rest, sedimentation of these particles promotes the formation of a layer of insoluble material at the bottom of the tank or where the biodiesel is stored.
The solid material observed in biodiesel consists of a mixture of compounds identified as comprising monoglycerides and steryl glycosides, which are primarily in the form of esterified steryl glycosides. When isolated, the steryl glycosides are in the form of a white powder, with a melting point between 240° C. and 290° C. and having reduced solubility in the majority of organic solvents, with the exception of pyridine and chloroform/methanol mixture (2:1).
Owing to the insolubility of the steryl glycosides in biodiesel, they become solid particles that are dispersed in the product, which influence the crystallization of other components in the product. It is thus necessary to purify the biodiesel obtained.
The set of equipment used in the steps associated with the purification of the product, to define it as biodiesel, is called the purification section. In this section, the light stream, rich in methyl and/or ethyl esters, received from a transesterification section, may be purified by techniques that can be divided into two main groups, known as wet washing and dry washing. The techniques belonging to the two groups have advantages and disadvantages and therefore selection of the most suitable method must basically comply with the criteria of product quality and process economy. Some techniques also possess the particular feature of having a hybrid character, i.e. they use both liquid fluids and adsorbent solid materials, combining them in different steps in order to meet the predetermined criteria.
In the dry purification of biodiesel, the light phase, received from the reaction section, only passes through columns with adsorbents, or through beds of ion-exchange resin, which provide removal of residual glycerol, traces of methanol and water present in the biodiesel, as well as soap, catalyst and salts. It is necessary to regenerate the adsorbents/resins and dispose of them when it is no longer possible to regenerate them. There are various suppliers of products for refining biodiesel by adsorption, each with their own technology and recommendations, such as LanXess, Rohm & Haas and Purolite.
On the other hand, the main technologies for purification of biodiesel in use in industrial units involve treatments with adsorbent materials, and may still require washing operations with water upstream of the step in which adsorption takes place. In all the technologies that employ washing of biodiesel with water, there is the option of using a subsequent refining step with filtration on a plate filter using a filter aid (for example diatomaceous earth), or using filtration systems consisting of self-cleaning filters and/or cartridge filters (high-flow cartridges and cartridges with adsorbent material). That is, in the purification of biodiesel the removal of water soluble contaminants is traditionally accomplished by water-washing the biodiesel. Another process of biodiesel purification involves the use of an “adsorbent filter-aid” such as magnesium silicate, and in the case of polar impurities it is usual to use a diatomaceous filter. The technology from Crown Technologies, for example, has two washing steps with water, followed by filtration on a plate filter, already containing a precoat, using diatomaceous earth as filter aid. However, this technology increases the cost of production and brings operational difficulties relating to the handling of solids, sometimes containing flammable substances, in the production unit.
Therefore, development of a process that dispenses with the use of a filter aid brings benefits in more than one aspect for the biodiesel plants.
In this connection, document US2011/0252397 relates to a process for obtaining biodiesel from fats, oils or fatty acids containing steryl glycosides. In this process, raw material is reacted by transesterification or esterification with short-chain alkanols in the presence of a catalyst, generating a fatty acid alkyl ester in a first product stream. Said first product stream is washed with water in a washing device, so as to form a layer of suspension at a phase boundary layer between a water-rich heavy phase and a first light phase rich in fatty acid alkyl ester. The layer of suspension is treated by stirring. A second product stream is withdrawn from the first light phase and mixed intensively with water to obtain a third product stream. Centrifugation is carried out on the third product stream to supply a fourth product stream and a fifth product stream. The fifth product stream is withdrawn as a heavy phase that is enriched with steryl glycosides. Product conditioning is carried out on the fourth product stream to obtain biodiesel that meets the specifications. In preferred embodiments, washing with water is carried out in countercurrent in a washing column. Product conditioning preferably comprises drying or filtration or both.
On the other hand, document US2013/0012732 describes a method for reprocessing a phase consisting substantially of steryl glycerides/fatty acid alkyl ester/water agglomerates, said phase being formed when fatty acid alkyl ester generated by the transesterification of vegetable oils or animal fats was washed with water, wherein the water content is evaporated by heating the phase and, subsequently, the steryl glycosides are split into their sterol and sugar fractions in the presence of an acid catalyst, both by adding a strong anhydrous acid and by contact with an acidic solid ion exchanger.
Moreover, document WO2007/076163 relates to processes for producing and treating biodiesel. This document proposes addition of an adsorbent or filter aid for separating steryl glycosides from the biodiesel and subsequent removal thereof by filtration, centrifugation or a combination thereof.
Thus, it can be seen that there are no documents in the prior art that disclose processes that purify biodiesel by a wet route without the need to use filter aids.